FBI officials took a man into custody after a security guard was shot at the downtown headquarters of the conservative Family Research Council on Wednesday morning.

Sources familiar with the incident told The Washington Examiner they believe the shooter had issues with the Christian group's support for "traditional marriage" and opposition to same-sex marriage. The FBI and D.C. police are investigating the incident and wouldn't comment on a potential motive.

A man walked into the FRC lobby at about 10:45 a.m. and was confronted by the security guard as per the organization's policy, D.C. Police Chief Cathy Lanier said. The man opened fire, and the guard was hit in the arm before he and others tackled the shooter, Lanier said. D.C. police said FRC security guards did not return fire in the incident, but neither the police nor the council would say whether the guards were armed.

"As far as I'm concerned, the security officer here is a hero," Lanier said. "The person never made it past him."

The suspect was uninjured and was taken into custody, Lanier said.

The wounded guard was taken to a hospital and was listed as being in stable condition on Wednesday afternoon.

The FBI identified the suspect as 28-year-old Floyd Corkins, of Herndon. Authorities and the FRC wouldn't comment on the shooter's motivation. The FBI said late Wednesday that he was being held on a charge of assault with a deadly weapon.

One knowledgeable source said the attacker was motivated "not just by FRC's policy but specifically their support for traditional marriage."

Police and FBI agents swarmed the 800 block of G Street NW on Wednesday morning, blocking off most of the street and, an FBI spokesman said, evacuating some staffers from the FRC building. Throughout the day, members of an FBI evidence team trailed in and out of the building wearing blue surgical gloves, as reporters and curious passers-by clustered on the street corner.

Amy and Steve Biondi, visiting from New York with their two daughters, said they were parking their car outside the FRC building when police ran past them into the lobby. Steve Biondi said he heard someone yell "Put the gun down!" and saw a man in a button-down shirt "go down."

"I said, you know what, let's just get back in the car," Amy Biondi said. "There was no time to be scared."

Bomb-sniffing dogs patrolled in the late morning outside the building, which authorities said was standard protocol. Just before 3 p.m., D.C. police cleared reporters and passers-by from G Street. An FBI spokesman confirmed that a suspicious package had been found in the FRC building, but the package was cleared within an hour.

FRC staffers who straggled out of the building at about 5 p.m. wouldn't comment on the incident. Anna Maria Hoffman, an FRC intern, tweeted shortly after the shooting, asking her followers to "please keep [the FRC] in your prayers."

FRC President Tony Perkins said in a statement: "Our first concern is with our colleague who was shot today."

News of the shooting spread fast among Washington-based conservative groups. Several immediately tightened security, including Americans for Tax Reform, which conducts a well-attended Wednesday morning meeting.

Paul Bedard and Scott McCabe of The Examiner contributed to this report.